A total of 18 survivors were pulled from the debris soon after the building toppled Friday Dar es Salaam, but none in last 46 hours the BBC reported. It wasn't clear how many people may remain trapped.
The British network said at least four people, reportedly the building owners and construction officials were being questioned by police.
Nishit Surelia, who witnessed the collapse of the building, which was to have been 12 stories high when completed, told the BBC the building made a "huge noise" as it fell.
"Everyone started running, thinking it was an earthquake," Surelia said. "There was dust everywhere. We then realized what had happened."